在线直播 from a Notebook
Live event streaming on a notebook can be the best of all worlds, with several programs available for free or relatively inexpensively, 而且一般来说很容易使用. But how powerful of a notebook do you need to stream effectively, 以及各种直播软件程序在CPU需求方面的比较, 数据速率精度, 数据速率一致性 and video quality? 最后, 这些节目的视频质量如何与硬件设备(如Digital Rapids TouchStream或ViewCast的GoStream SURF)制作的视频质量相匹配? In this article, I'll attempt to answer all of these questions.
Specifically, I tested three notebooks: a 2.2 Core2Duo-based Hewlett Packard 8710w, a 3.06 Ghz Core2Duo-based MacBook Pro and a 2.0 four-core (8 with HTT) i7-based Hewlett Packard 8740w. 我还测试了四款软件:Adobe Flash Media Live Encoder(免费), Kulabyte XStream 2 (around $10,000), Microsoft Expression Encoder 4 ($199.95) and Telestream Wirecast ($495). I realize there are other programs that I could have tested, 但这些似乎是直播市场空间中最受关注的. 如果你不同意，请告诉我，因为这不会是我们关于这个主题的最后一篇文章.
我是如何测试的
我测试了标清和高清输入，在三台电脑上都测试了标清输入，只在HP 8740w上测试了高清输入. 对SD, I tested using my standard 5:50 minute 4:3 SD test file, 我输出到DV磁带, 并通过火线将我的佳能XH A1摄像机的数据反馈到不同的电脑上.
我测试了5种SD场景. 第一个 I did standalone encodes at 640x480@700Kbps, 480x360@400Kbps. 和320x240@200Kbps，都是原生帧率，都是32Kbps的单声道音频. 然后，我通过生成两个最低分辨率的流(480x360)来模拟自适应流的生产 & 320x240)同时进行，如果有可能的话，所有三个流. 请注意，对于这些测试，我将所有文件捕获到磁盘，而不是将它们流式传输到服务器.
I used each program's default settings as much as possible, 因为这些应该代表软件开发人员对最佳设置的看法. 有趣的是，对于H.264编码, 我只测试了这个, Adobe defaults to the Baseline profile, 微软高调出击, and Telestream to the Main profile. 稍后会详细介绍.
HD测试, I used several HD source tapes, including an interview with former Congressman Rick Boucher, and some rehearsal footage of Virginia bluegrass band No Speed Limit. For HD, I tested two scenarios; first, a four stream test (1280x720@2Mbps, 848x480@1.5 mbps, 640年x360@800kbps, 和480年x270@500kbps, 所有在64Kbps音频和本机帧率)和一个单一的流848x480@1.5 mbps test, again with 64Kbps audio and native frame rate. For all HD tests on all programs, 我使用连接到8740w的Express card插槽的BlackMagic Decklink卡捕获, capturing component video and analog audio input.
我将展示结果如下:首先，我将查看使用SD和HD场景的各种程序的CPU效率, 它会告诉你哪些程序实际上可以在每个平台上产生必要的流. Then I'll look at 数据速率精度, 数据速率一致性, and the video file quality produced by the programs.
CPU效率
To test CPU utilization with SD, I queued up Performance Monitor, 将测量时间延长至20分钟左右，并在所有测试场景中捕获三分钟的视频. This yielded a chart like that shown in 图1 对于每个程序. 很明显, 这些结果将告诉您是否可以使用所需的程序在笔记本上生成所需的流配置.
图1. 这张来自Performance Monitor的图表显示了Telestream Wirecast在所有五个测试中的CPU利用率.
8710w
在惠普8710w上, 我测试了Adobe FMLE, Expression Encoder 4 and Telestream Wirecast, 没有提到Kulabyte，因为该公司的目标是需要更强大电脑的高清网络活动. 表1 shows the results garnered from the individual CPU utilization graphs, which illustrate the percentage of CPU required for each task.
关于结果的一些说明. 第一个, 通过/失败指定表示在捕获的文件中存在重要的丢失帧. 用FMLE和EE4, 这很简单, 因为这两个程序都提供了丢弃帧计数器，当你开始丢弃帧时，它会立即让你知道.
相比之下，Wirecast显示的是有效捕获率，它随秒而变化. To check the suitability of the files captured by Wirecast, I checked the frame rate after capture in MediaInfo, and all files were at least 26.98 frames per second or higher. I supply more on the effective frame rate captured by Wirecast below.
| | 640x480 | 480x360 | 320x240 | 480&320 | 所有 |
Adobe FMLE | 100% -失败 | 65-75% -通过 | 45-60% -通过 | 100% -失败 | 二硝基酚 |
微软EE4 | 100% -不及格/ 85-95% -通过 | 75-98%及格/ 85-90%及格 | 50-60%通过/70-80%通过 | 100% -失败 | 二硝基酚 |
Telestream Wirecast | 55-75% -通过 | 40-55% -通过 | 30-40% -通过 | 40-75% -通过 | 90-95% -通过 |
表1. CPU utilization by the respective programs.
第二个, I tested twice with Expression Encoder 4, 使用和不使用GPU编码, because it made a substantial difference in quality and performance. Performance you can see in the table; in terms of quality, check out 图2. Though the difference in quality was slight in low motion footage, 当行动加速时, GPU-based encoding degraded rapidly. Unless you're producing purely talking heads, 在微软计划于2011年发布的Main Concept解决这个问题之前，只能指望使用基于cpu的编码.
图2. With moderate motion, GPU-based encoding in EE4 degrades rapidly.
By the way, I tested EE4 using the Baseline profile instead of High. Though CPU utilization stayed around 100%, EE4 was able to capture the 640x480 stream reasonably successfully, dropping 388 of 5882 for an effective frame rate of just over 25 fps. If you're producing with a slightly faster notebook, 你可以试一试, 但运行在或接近100%的CPU利用率似乎是一个坏主意的直播.
I also tested the Adobe Flash Live Media Encoder in Main mode; which bumped CPU utilisation a hair, but made very little difference in quality. 郑重声明, I tested Wirecast with GPU-acceleration enabled, 但这对质量和CPU要求都没有什么影响.
来解释结果, 如果你想在基于Core2Duo的笔记本电脑上获得全质量的640x480输出, 无线广播是你最好的选择, 尽管Expression Encoder 4可以在说话头场景中完成工作，您可以使用gpu协同处理, or with a faster notebook capturing in the Baseline profile. 所有 programs can produce at 480x360, 但是Wirecast是你为自适应比特率流生成多个文件的唯一选择.
MacBook Pro
Here we get to the bait and switch portion of the review; well, kinda anyway. 我的意思是，我只能在MacBook Pro上运行一个程序，那就是Wirecast. 我有一个版本3.在笔记本上加载了1个Adobe FLME，但卸载了它以加载版本3.2、其中拒绝安装. I tried going back to version 3.1, but that wouldn't install either. I enlisted Adobe's help, but still couldn't get it running. I know that failing to test FMLE will disappoint many Mac producers, 这是理所当然的, but hopefully I can rectify the situation in a subsequent review.
图3. Wirecast CPU utilization on the MacBook Pro.
不管怎么说, 图3 显示MacBook Pro的CPU历史记录窗口，用于我的Wirecast测试. 如你所见, the Mac was quite handy with Telestream, seemingly slightly more efficient than the HP 8710w, which makes sense since the Mac has a 3.06 GHz CPU as compared to the HP's 2.2 GHz处理器.
The MacBook Pro and Wirecast performed very well together, 在单个文件测试中生成的所有文件以每秒29帧或更高的速度呈现. 所有 files produced during the latter two tests had a frame rate of 28.2 FPS或更高. 只有眼光最敏锐的人才能看出有什么画面掉下来了.
8740w
在8740w上，我添加了Kulabyte XStream 2，通过BlackMagic Decklink卡捕获. 在这台计算机上，我在禁用GPU的情况下测试了Expression Encoder 4. 我在 表2.
| | 640x480 | 480x360 | 320x240 | 480&320 | 所有 |
Adobe FMLE | 18-22% | 15-18% | 15-18% | 20-25% | 40-60% |
Kulabyte XStream 2 | 12-15% | 10-12% | 7-10% | 15-20% | 18-25% |
微软EE4 | 22-32% | 18-22% | 15-18% | 15-25% | 35-55% |
Telestream Wirecast | 12-18% | 10-18% | 10-12% | 15-18% | 18-25% |
表2. CPU utilization by the respective programs.
如你所见, throwing CPU horsepower at the problem definitely helps resolve it, as from a CPU utilization percentage, 基于i7的HP绝对可以从所有程序访问所有流和流的组合. 这里没有通过/失败-所有程序产生的流没有下降明显的帧量.
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